Method of preparing cellulose-ester products



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' HARRY s. MORE, or BROOKLINE; Ann CHARLES r. corrm, JR.-, or W'AtrER rowN' MASSACHUSETTS, ASSIGNORS TO THE LUSTRON COMPANY, OF SOUTH BOSTON, MASSACHUSETTS, A VOLUNTARY ASSOCIATION OF MASSACHUSETTS.-

METHOD or PREPARING CELLULOSE-ESTER raonuc'rs.

To aZZ- whom it may concern:

Be it known that we, (1) HARRY S. Mom: and (2) CHARLES F. CoFrIN, Jr., citizens of the United States, residing at (l) Broo kline, (2) Watertown, in the counties of (1) :Nor-

folk, (2) Middlesex, and State of Massa-- chusetts, have invented certain new and useful Improvements in Methods of Preparing Cellulose-Ester Products, of which the following is a specification.

This invention relates to methods for the preparation of cellulose ester products of predetermined and standardized dyeing speed. By cellulose esters we mean particu-' larly such substances as cellulose acetate, butyrate and propionate.

The standardization of the dyeing speed in the sense in which the expression is used herein does not consist in adding retardants or assistants to the dye bath, or in governing the time and temperature during dyeing; but the dyeing speed (or in other'words the dye absorption rate) as the term is used herein is an inherent property of the undyed cellulose ester or of the product derived therefrom when the same is prepared in accordance with this invention.

The standardization of the dyeing speed can be secured to a greater or less degree in three different ways, or by certain combinations thereof,,viz

(a) By exercising a practical method of control of the conditions of the chemical reaction by which the cellulose ester is produced. v

(b) By suitably treating each batch of cellulose ester or cellulose ester product after it has been produced in order to bring it to a predetermined dyeing speed.

(a) By combining lots of non-identical dyeing speeds in relative proportions to p'ro- .duce' aproduct having a desired dyeing speed.

For the purpose of detailed description of our invention in so'far asit relates to the primary reaction, we will illustrate itby showing its application to the manufacture of cellulose acetate and products resulting from the subsequent manipulation of cellulose acetate. Also for the purpose of illustration ,United States Patent No. 854,374, May 21 Specification of Letters Patent. Patented June 2%, 1%22,

Original application filed March 12, 1921, Serial. No. 451,846. Divided and this application filed November16, 1921. Serial No. 515,630.

r we will describe it with reference to the manufacture of cellulose. acetate according to 1907, to 11.8. Mork.

The above patent-covers the. process of making what is now, termed fibrous cellulose acetate or a tyipe of cellulose acetate in which the original orm of the cellulose used is substantially conserved. In the commercial conduct of this process it has heretofore been the custom to govern the conditions of the process, viz, proportion of. condensing 7 agents, time, temperature, proportions of restraining agent, etc., solely from thepoint of view of obtaining final acetylation products of desired solubility, viscosity, mechanical strength, elasticity and durability. We believe 1n fact that heretofore all fundamental cellulose reactions have been carried out with these objects in view. a

Now for certain purposes, as for example the manufacture of artificial silk, it is-not only important to controlin the primary cellulose acetate all the properties above men? tioned, but it is also desirable to control the conditions of the reaction so that different batches of the estershall in so far as is practically possible exhibit a definite behavior when subjected to a subsequentprocess of be- I ing dyed dyes or dystufls for which the cellulose compound may have a specific af. finity.

Cellulose acetate and cellulose acetate products made therefrom, as for example,

.cellulose acetate artificial silk, have peculiar dye aliinities and dye resist properties, in that unmordanted cellulose acetate has a very strong aflinity for the basic dyes, for example methylene blue and auramine, and at the.

same time practically no atfinity for the direct cotton or benzidine dyes. Unlike the animal fibres, it has for the acid dyes.

In the ordinary conduct of theMork process mentioned above, wherein successive batches of cellulose acetate produced thereby all-show this'characteristic affinity for basic dyes and lack of aflinity for the direct cotton dyes, successive batches are apt to exhibit decided differences in the rate at which they practically no afiinity tion of the cellulose acetate or cellulose acetate product thereby produced, as preferably by a combination of these methods.

' Unmordanted cotton has practically no affinity for the basic dyes, but when subjected discovered that as the acetyla-tion proceeds from its early stages, whereas the acetylated cotton still maintains its capacity of being dyed to full shades by basic colors, there is a peculiar lessening as the process proceeds towards complete acetylation of the rate at which the cellulose acetate will be dyed by the basic colors.

If the acetylation process'is conducted solely from the point of view of producing difl'erentbatches of cellulose acetate of uniform or specific solubility and viscosity, these characteristics can readily be 1)]?0". duced; but unless other precautions are taken these different batches may absorb basic dyes at widely difi'ering rates. This property of differential dyeing rate will follow through to any products made from these different batches of cellulose acetate; so that if it is desired to manufacture artificial silk therefrom, one lot may dye at one rate and another lot may dye at another rate. When these different lots of artificial silk are mined, as they always will be in commercial textile operations, even if great precautions are taken dyed yarns or fabrics will be produced which will show streaks and irregularities, which in most cases are highly undesirable and render the material unsaleable. being able to produce cellulose acetate prodnets of uniform dyeing rate is very obvious.

Whereas in ordinary acetylation procedures it is the practice to control the solubility and the viscosity of the cellulose ace tate by regulating the amount and character of the condensing agent, the temperature and the reaction time, in order to. lessen the dyeing speed differences between successive batches of cellulose acetate particular attention must be given to the quan- The advantage, therefore, of.

tity of acetic anhydrid used and to the time of reaction. use an amount of acetic anhydrid in excess It is the uniform custom to of that theoretically required to produce in one case the amount of anhydrid used in the acetylation was only slightly in excess of the theoretical quantity necessary, while in the other case it was very considerably in excess of the theoretical amount of acetic anhydrid necessary. The cellulose, acetate produced in the first instance will be a very much .more rapid, dyer than that produced in the second instance. For example, in the first instance the cellulose acetate might exhaust a dye hath made up with 1 5% by weight of methylene blue in two or three minutes at normal temperature, whereas in the, second instance eight or ten minutes might be required. Inasmuch as each of these lots if dyed separately and given sufficient length of dyeing will completely ex haust the dye bath, the color of both of them after dyeing would be the same. On the other hand if a mixture of these two lots of cellulose acetate are dyed together in the same dye bath, it will be found that when the dye is exhausted the-fastdyer will be dyed a very deep shade and the slow dyer will be dyed a very pale shade.

If these particular lots cited above are individually dissolved in suitable solvents and manufactured into different lots of artificial silk, the silk produced from the fast dyeing lot of cellulose acetate will dye more rapidly than the silk produced from the slow dyeing lot of cellulose acetate. c

As indicated above, within the limits of good solubility fast dyers and slow dyers can be produced. Convenience of operation would dictate that a standard .be adopted at some point within the solubility range which was neither at the fast dyeing limit or the slow dyeing limit.

We have also stated our discovery of the fact that within the solubility range, the morecomplete the acet-ylation the slower is the dyeing rate. But we have further found that the dyeing rate of slow dyeing cellulose esters and cellulose ester products can be accelerated by a suitable de-esterit'ying treatment, such for example as treatment with aqueous solutions of either alkalics or mineral acids, either hot or cold. The accelera tion of the dye rate progresses gradually, and we have found by experiment that it.is possible to arrest the treatment at a predetermined dye rate standard with commercial accuracy.

If the fibrous cellulose acetate is to be used in 1 its original acetylated fibrous form for textile constructive purposes, it is necessary that all the batches should be acetylated uniformly to a predetermined dye rate standard,

which is an exceedingly diflicult commercial operation; or preferably all the batches can be acetylated until they have a dye rate equal to or slower than the predetermined standard, and then those batches havin a slower dye rate can be treated as herein efore indicated to bring them to the desired dye rate or to any desired approximationthereto.

If different batches of cellulose acetate which have not been standardized. as to the dye rate are converted by means of solvents into products such as films, artificial silk and so forth these latter can also be treated as described until they acquire the desired dye rate.

WVe have discovered, however, another 'method of standardizing the dye rate of colloided or conversion products of the original cellulose acetate, such as filaments, etc.

Inasmuch as the manufacture of films-and filaments involves working the celluloseacetate into a practically'homogeneous mass by treatment with a solvent-or'plasticizer or Y both, it ispossible during such treatments to mix or blend cellulose acetates of different dye rates. We have, found thatit is possible to measure the comparative dye rates of different lots of cellulose acetate, and then to blend these different lot-s according to the dye rate measure to produce a conversion product, as for example, a plastic mass, film or filament of any desired dye rate standard. We have foundthat a blend of two or more different lots of cellulose acetate of not widely varying dye rates will have a dye rate very close to the numerical average of the dye rates of the individual lots; but that when the different lots in the 'blend have widely different dye rates, then the dye rate of the blend departs somewhat from the mathematical average of the individual lots. In thislatter case,-proportio ns necessary to blend to procure a standard dye rate must be determined by test, although it is probable that when more data is available a matheferential dyeing rates of different lots of cellulose acetate and means of standardizing the dye rate, that we have made a dlscovery sired predetermined dyeing speed.

not only of fact but of broad principle andof vital importance to industries based on the manufacture and use of cellulose compounds, such as the manufacture ofcellulose acetate silk. This principle of dye control is not only applicable to cellulose ace tate and cellulose acetate products but also v to the production of, and use of any allied cellulose compounds where like variabilities exist.

It will be further evident from the foregoing that various combinations of the several standardizing methods may be employed dyeing speed. Also, as stated above,the deesterification or after-treatment of slow dyeing batches may be applied if desired to'the final product, for example artificial silk. I

We do not claim herein the method described according to -whichthe batches of cellulose ester in the presence of a solvent are combined 'in relative proportions to produce a homogeneousv product having the de- This method is claimed in our co-pe'nding application Serial No. 451,846,. filed March 12,

1921, of which the division.

Also, the embodiment of the invention wherein several batches of silk are prepared and the batches of slower dyeing speed subpresent application is a jected to an after-treatment to effect subi stantial equalization of the dyeing speeds of the several batches is not herein specifically claimed. but is the subject of a separate application filed by us on November 16,1921,

Serial No. 515,631, which is also a division of our earlier application, Serial No. 451,846, filed March 12, 1921.

We claim 1. Method of preparing cellulose ester products of standardized dyeing speed, com prising preparing several batches of the ester; subjecting ba-tches of slower dyeing speed to an after treatment to effect substantial equalization of the dyeing speeds of the .several batches; and then combining the batches in the presence of a solvent.

2. Method of preparing cellulose ester products of standardized dyeing speed, comprising preparing separate batches of the ,ester; subjecting batches of slower dyeing speed to a de-esterifying treatment to effect partial equalization of the dyeing speeds of the several batches; and then combining the batches in presence of a solvent and in relative proportions to produce a homogeneous product having the desired predetermined dyeing speed.

3. In a method of preparing cellulose est/er ing batches of slower dyeing speed to a deesterifying treatment to effect at least partial equalization ofthe dyeing speeds of the several batches.

In testimony whereof, we affi); our signa tures.

HARRY S. MORK. CHARLES F. OOFFIN, JR. 

